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What if light passes from lighter to denser medium

  1. Sep 18, 2012 #1
    hello guys,
    i need your help to clear my concept on total internal reflection ....when incident ray angle is greater than the critical angle for light passing through denser to lighter medium the total internal reflection occurs...and i know about corresponding snell equation and its validity conditions

    now what if i reverse the situation for light passing through lighter to denser medium , then is there any possibility the reflective ray makes 0 degree angle with the normal for a particular incident ray angle??...then what the angle be called ??

    and what if the incident ray angle crosses that particular incident ray angle then what will be the consequence of the refection ??
    ( i know mathematically snell's law says no total internal reflection, but let me know the ultimate consequence of this icident ray )

  2. jcsd
  3. Sep 18, 2012 #2


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    Staff: Mentor

    In such a case it's just normal reflectance from an optical surface. The larger the angle the greater amount of light reflected instead of transmitted. As the angle of incidence approaches 90 degrees you have whats called glancing incidence, in which practically all the light is reflected from almost any smooth surface, irregardless of the material. At 90 degrees no light is transmitted, all of it is reflected.

    A good estimation of the losses in an optical system is given by : R= (1-n/1+n)2
    With n = 1.5 you come up with a value of about 4% loss from light moving from air into glass at normal incidence (0 degree angle)
  4. Sep 19, 2012 #3
    Yes, that "particular" incident angle is zero degrees. Light normal to the surface is reflected back along the normal. Not all light is reflected, though. Some will enter the second medium, along the normal too.
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